Shell holder



FIG. 1 is a perspective view of a shell holder embodying the invention;

FIG. 2 is a front view of the shell holder of FIG. 1; and,

FIG. 3 is a right side view of the shell holder of FIG. 1.

The broken lines showing the environment is for illustrative purposesonly and forms no part of the claimed design.

The ornamental design for a shell holder, as shown and described.